Biology MCQs

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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Page 35 of 103
Question #681
The largest gland in the human body is the:
A. Thyroid
B. Liver
C. Spleen
D. Pancreas
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Correct Answer: Option B

Explanation:
The liver is the largest internal organ and gland, weighing about 1.5 kg in an adult. It performs over 500 functions, including bile production, detoxification, metabolism of carbohydrates, lipids, and proteins, and synthesis of plasma proteins. The pancreas and thyroid are smaller glands, the spleen is not a gland.
This question belongs to: Science Biology
Question #682
The term for a sequence of three nucleotides on mRNA that specifies an amino acid is:
A. Intron
B. Anticodon
C. Exon
D. Codon
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Correct Answer: Option D

Explanation:
A codon is a triplet of nucleotides in mRNA that codes for a specific amino acid or signals termination of translation. There are 64 codons; 61 code for amino acids and 3 are stop codons. Anticodons are on tRNA, exons are coding regions of DNA, introns are non-coding.
This question belongs to: Science Biology
Question #683
The process of physical and chemical breakdown of food into absorbable form is:
A. Absorption
B. Assimilation
C. Egestion
D. Digestion
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Correct Answer: Option D

Explanation:
Digestion converts complex, insoluble food molecules into simple, soluble forms that can be absorbed. It involves mechanical action (chewing, churning) and enzymatic hydrolysis. Absorption is the uptake of nutrients, assimilation is incorporation into body tissues, egestion is elimination of undigested waste.
This question belongs to: Science Biology
Question #684
The vitamin whose active form, retinol, is essential for vision is:
A. Vitamin E
B. Vitamin D
C. Vitamin C
D. Vitamin A
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Correct Answer: Option D

Explanation:
Vitamin A (retinol) is converted to retinal, which combines with opsin to form rhodopsin, the light-sensitive pigment in rod cells of the retina. Deficiency leads to night blindness and xerophthalmia. Carrots and liver are rich sources. Vitamin C is ascorbic acid, D is calciferol, E is tocopherol.
This question belongs to: Science Biology
Question #685
The organ that produces digestive enzymes and insulin is the:
A. Spleen
B. Pancreas
C. Liver
D. Gall bladder
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Correct Answer: Option B

Explanation:
The pancreas is a mixed gland: exocrine acini secrete digestive enzymes (trypsin, lipase, amylase) into the duodenum, while endocrine islets secrete insulin and glucagon into the blood. The liver produces bile, not digestive enzymes. Spleen filters blood, gall bladder stores bile.
This question belongs to: Science Biology
Question #686
The type of circulatory system in which blood is confined to vessels is called:
A. Lymphatic system
B. Open circulatory system
C. Portal system
D. Closed circulatory system
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Correct Answer: Option D

Explanation:
In a closed circulatory system (e.g., humans, annelids, cephalopods), blood is always enclosed within vessels (arteries, veins, capillaries) and is distinct from interstitial fluid. Open systems (arthropods, most mollusks) have hemolymph bathing organs in sinuses. The lymphatic system returns fluid to blood. A portal system connects two capillary beds.
This question belongs to: Science Biology
Question #687
The protein that carries oxygen in muscles is:
A. Hemoglobin
B. Ferritin
C. Myoglobin
D. Transferrin
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Correct Answer: Option C

Explanation:
Myoglobin is an oxygen-binding protein in muscle cells, containing a single heme group. It has a higher affinity for oxygen than hemoglobin, facilitating oxygen diffusion and storage in muscles. Hemoglobin is in blood, ferritin stores iron, transferrin transports iron.
This question belongs to: Science Biology
Question #688
The phenomenon of a single gene affecting multiple traits is called:
A. Polygenic inheritance
B. Epistasis
C. Pleiotropy
D. Multiple alleles
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Correct Answer: Option C

Explanation:
Pleiotropy occurs when one gene influences several distinct phenotypic traits. Example: phenylketonuria (PKU) caused by a single gene defect leads to mental retardation, light skin color, and musty odor. Polygenic inheritance is many genes affecting one trait, epistasis is gene interaction, multiple alleles are more than two alleles for a gene.
This question belongs to: Science Biology
Question #689
The element that is a key component of the thyroid hormones T₃ and T₄ is:
A. Iron
B. Iodine
C. Phosphorus
D. Calcium
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Correct Answer: Option B

Explanation:
Iodine atoms are incorporated into thyroxine (T₄, 4 iodine atoms) and triiodothyronine (T₃, 3 iodine atoms) synthesized by thyroid follicular cells. Iodine deficiency leads to goiter and hypothyroidism. Iron is in hemoglobin, calcium in bones, phosphorus in ATP and bones.
This question belongs to: Science Biology
Question #690
The structure in the chloroplast that is the site of the light-dependent reactions is the:
A. Thylakoid membrane
B. Stroma
C. Inner membrane
D. Outer membrane
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Correct Answer: Option A

Explanation:
Light reactions occur in the thylakoid membranes, where photosystems I and II, electron transport chains, and ATP synthase are located. Light energy is captured to produce ATP and NADPH and split water. The Calvin cycle (light-independent) occurs in the stroma.
This question belongs to: Science Biology
Question #691
The hormone that promotes the development of the corpus luteum after ovulation is:
A. FSH
B. LH
C. Estrogen
D. Prolactin
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Correct Answer: Option B

Explanation:
Luteinizing hormone (LH) triggers ovulation and then promotes the formation and maintenance of the corpus luteum from the ruptured follicle. The corpus luteum secretes progesterone. FSH stimulates follicle growth, prolactin milk production, estrogen from follicles.
This question belongs to: Science Biology
Question #692
The process of uptake of liquid droplets by the cell membrane is:
A. Osmosis
B. Phagocytosis
C. Exocytosis
D. Pinocytosis
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Correct Answer: Option D

Explanation:
Pinocytosis ('cell drinking') is a form of endocytosis where the cell membrane invaginates to take in a small droplet of extracellular fluid and dissolved solutes. Phagocytosis is 'cell eating' of large particles, exocytosis is secretion, osmosis is water movement across a semipermeable membrane.
This question belongs to: Science Biology
Question #693
The scientist who discovered the penicillin-producing mold was:
A. Joseph Lister
B. Robert Koch
C. Alexander Fleming
D. Louis Pasteur
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Correct Answer: Option C

Explanation:
Alexander Fleming noticed in 1928 that a mold contaminant (Penicillium notatum) on a bacterial culture plate inhibited the growth of Staphylococcus aureus, leading to the discovery of penicillin, the first widely used antibiotic. Florey and Chain later purified it. Pasteur developed pasteurization.
This question belongs to: Science Biology
Question #694
The tissue that forms the outer protective covering of the plant body is:
A. Vascular tissue
B. Meristematic tissue
C. Ground tissue
D. Dermal tissue
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Correct Answer: Option D

Explanation:
Dermal tissue (epidermis in primary growth, periderm in secondary growth) forms the outermost protective layer of leaves, stems, and roots. It includes specialized cells like guard cells and root hairs. Vascular tissue (xylem, phloem) conducts, ground tissue fills and stores, meristematic is for growth.
This question belongs to: Science Biology
Question #695
The disease caused by the bacterium Vibrio cholerae is characterized by:
A. Bloody diarrhea
B. High fever and rash
C. Severe watery diarrhea (rice-water stools)
D. Persistent cough
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Correct Answer: Option C

Explanation:
Cholera, caused by Vibrio cholerae, produces cholera toxin that stimulates massive secretion of water and electrolytes into the intestinal lumen, leading to profuse, watery diarrhea resembling rice water, causing rapid dehydration. Treatment is oral rehydration therapy and antibiotics. Typhoid causes fever, dysentery causes bloody stools.
This question belongs to: Science Biology
Question #696
The function of the myelin sheath is to:
A. Produce neurotransmitters
B. Decrease the speed of nerve impulse
C. Store energy for the neuron
D. Insulate and increase the speed of nerve impulse conduction
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Correct Answer: Option D

Explanation:
Myelin, a lipid-rich sheath formed by Schwann cells (PNS) or oligodendrocytes (CNS), insulates axons, allowing saltatory conduction—impulses jump from one node of Ranvier to the next, greatly speeding up transmission. It also conserves energy. Demyelinating diseases like multiple sclerosis slow conduction.
This question belongs to: Science Biology
Question #697
The enzyme that converts angiotensinogen to angiotensin I is:
A. Pepsin
B. Renin
C. Trypsin
D. ACE (angiotensin-converting enzyme)
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Correct Answer: Option B

Explanation:
Renin, released by juxtaglomerular cells of the kidney when blood pressure drops, cleaves angiotensinogen (from liver) to angiotensin I. ACE then converts angiotensin I to the active angiotensin II, a potent vasoconstrictor and stimulator of aldosterone. Pepsin and trypsin are digestive proteases.
This question belongs to: Science Biology
Question #698
The specific gravity of normal urine is approximately:
A. 1.050-1.100
B. 0.800-0.900
C. 1.000
D. 1.015-1.030
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Correct Answer: Option D

Explanation:
Urine specific gravity, a measure of solute concentration, normally ranges from 1.015 to 1.030. It varies with hydration status: low when dilute (after drinking), high when concentrated (dehydration). Diabetes insipidus shows low SG, diabetes mellitus may show high due to glucose.
This question belongs to: Science Biology
Question #699
The organelle that contains catalase and peroxidase enzymes is the:
A. Peroxisome
B. Golgi apparatus
C. Mitochondria
D. Lysosome
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Correct Answer: Option A

Explanation:
Peroxisomes are single-membrane organelles containing oxidative enzymes like catalase and urate oxidase. They break down fatty acids via β-oxidation and detoxify hydrogen peroxide. Lysosomes contain hydrolytic enzymes, mitochondria energy, Golgi packaging. Peroxisomes are abundant in liver and kidney cells.
This question belongs to: Science Biology
Question #700
The blood vessel that carries oxygenated blood from the placenta to the fetus is the:
A. Aorta
B. Pulmonary artery
C. Umbilical vein
D. Umbilical artery
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Correct Answer: Option C

Explanation:
The umbilical vein carries oxygen-rich and nutrient-rich blood from the placenta to the fetal circulation. The two umbilical arteries carry deoxygenated blood and waste from the fetus to the placenta. In the adult, veins typically carry deoxygenated blood, but umbilical vein is an exception.
This question belongs to: Science Biology

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